Flat bottom plastic bags are known.
In such flat bottom plastic bags, it is necessary to form a folding axes so that upon bag opening, the flat bottom of the bag hinges along diagonal fold lines to "square out" and form an upstanding bag structure for the receipt of articles to be placed in the bag. In addition to paper bags in commerce, exemplary of the prior art is:
Platz et al U.S. Pat. No. 3,917,159 takes an already manufactured bag and folds the bottom so that it will "square out."
Le Fleur et al U.S. Pat. No. 3,915,077 utilizes individual heat seals to form the "squared out" portion of the bag.
Hanson et al U.S. Pat. No. 3,988,970 discloses a bag process where a square bottom bag is first produced. Thereafter, the bag is folded so that the plastic film emulates the folding present in ordinary paper bags. This folding process occurs after the square bottom bag is fully manufactured.
Ross et al relates to a plastic bag that utilizes among other constitutents glue.
In the disclosure that follows, a plastic bag is manufactured which uses either "cold seals", hinges, and/or hybrid cold seals and hinges in plastic film for the rapid production and formation of a plastic bag. It is important that the reader understand both of the "cold seal" and "hinge" terms and how they are limited in the disclosure that follows.
First, it is important to understand that in modem plastic bag manufacturing technology, speed of film processing is essential. In a typical bag manufacturing process, film passes through a machine for bag manufacture at rates up to 300 feet per minute is required for economic manufacture. Further, each manufacturing step must anticipate the subsequent opening and loading of the bag. As a consequence, steps taking an inordinate amount of time slow down the bag line speed and are generally unacceptable. Further, any bag post-production step--such as folding an already manufactured bag--is unacceptable.
Because of this speed requirement, so-called "hot seals" are generally not acceptable for any portion of the bag that does not require full strength sealing. In a hot seal, one film layer of a bag is permanently fused to another film layer of a bag. Hot seals take time to produce. Melting must be sufficient for complete fusing to take place between the bag parts. As a result, a hot seal is a significantly slower method of plastic bag manufacture than either utilizing a "cold seal" or forming a "hinge" within plastic film.
In a hot seal application transverse to the direction of film conveyance during plastic film bag manufacture, line speeds of the passing plastic film are usually limited to 150 feet per second. In the manufacture of the disclosed bag, line speeds in the range of 300 feet per second can be tolerated.
Hot seals produce permanent fusing of the plastic layers involved. Such permanent fusing can be detected by trying to separate the joined film layers. When such an attempt is made to separate the two layers joined by a hot seal, either joined film layer tears. The "hot seal"--composed of two layers fused one to another--does not tear and remains in tact.
Regarding the use of a "cold seal", in the plastic bag manufacturing arts, there has been known for many years a defective seal known as a "cold seal." Such a cold seal has here to fore been an imperfect hot seal. Usually, the imperfect hot seal would be located at the bottom of a plastic bag. When load was placed in the plastic bag, the seal would part--and the bag contents drop to the ground, usually causing content loss and damage.
Cold seals as used in the specification that follows are easy to distinguish. Where a cold seal is present, it imperfectly seals two plastic film layers together. This imperfect fusing can be easily recognized. Film separation at the cold seal allows the two imperfectly fused film layers to separate. Each layer separates from the other layer without losing substantial structural integrity of the film. Unlike the conventional "hot seal", neither of the previously fused film layers tears when separation occurs.
Cold seals have been used with plastic bags for joining bags loosely in a bundle. Such joinder usually takes place at the top of the bag adjacent the opening. In the typical application, separation of a bag from a bundle of bags at a cold seal usually assists in the opening of the bag.
Until this disclosure, no one has made a "cold seal" an important structural element of a bag!
In addition to the "cold seal", this disclosure makes use of a preformed "hinge" with the plastic film of the bag wall. Such hinges are capable of rapid formation by impressing the rapidly passing and planar film along a linear boundary. This impressing at the linear boundary leaves the film predisposed to "hinge" or fold at the boundary.
The hinge that is here utilized is to be distinguished from a "fold." In folding, film is bent over and then creased so that it folds. Once this bending and creasing has occurred, the film is disposed to repeat the bending and folding along the crease.
The "hinge" here utilized is place in the plastic film of the bag wall while the film is planar or in the "lay flat condition--and passes through the bag machine at high speed. The placed linear hinge is typically either at right angles to the direction of film motion or alternatively diagonal to film motion. Thus the hinge here used, is not to be confused with side gusset creases that result from creased folds made in the direction of film passage. When the film is hinged--for the first time from the lay flat state to the erect disposition of the bag--the hinge structure impressed in the film predisposes the film to bend along the hinge axis. Through the combination of the hinge joining panels of plastic across the multiple flat surfaces of an erect bag, sufficient structural integrity is imparted to the bag to remain upright and open to receive and contain articles--such as fast food orders.
The front panel, rear panel and gusset panels each include a plastic film having a predetermined thickness sufficient for the plastic film to remain planer in an absence of a first bending moment applied across the plastic film. The hinge includes at least one linear groove configured in the plastic film to reduce the predetermined thickness of the plastic film at the linear groove and to permit preferential hinging of the plastic film at the linear groove. Such hinging occurs responsive to a bending moment. This is because the linear groove has insufficient depth to sever the plastic film and retains sufficient remaining thickness at the linear groove to permit hinging and not tearing of the plastic film at the linear groove.
The reader should also understand that the difference between a "cold seal" and a "hinge" is not always precise. For example, where plastic film is passing a die at relatively high speed, and the dye come down upon two or more layers of plastic film, a hybrid "cold seal and hinge" can result. The cold seal will be recognizable by the imperfect fusing of the plastic layers one to another. The hinge will be recognizable by the reduction in thickness of the plastic film wall with the increased tendency of the film to fold at the hinge. It has been found that hybrid "cold seal" and "hinge" structures are produced in the bag production process herein set forth.
In the disclosure that follows, neither the "cold seal" nor the "hinge" incorporate or refer to bending and creasing film so that the film may bend again along the bend or the crease. In both the cases of the "cold seal" and "hinge", the film is at all times flat and planar when the "cold seal" or "hinge" is applied and introduced. This is known as the "lay flat" condition.